Project Summary/Abstract For many pregnancies, there are few effective ways to treat placental diseases that result in fetal demise, poor fetal outcome and/or increased risk of fetal programing of adult onset disease. Poor placental function is a contributing cause of pregnancy related diseases, including intrauterine growth restriction (IUGR) and preeclampsia (PE). Despite decades of research investigating pregnancy and fetal outcome, there is no true understanding of how the basic biological processes involved in placental development fail. Aberrant trophoblast cell proliferation and differentiation have been considered responsible, however the etiology is not understood and in many cases, obstetricians can only manage the mothers' symptoms. Although persistent proliferation of trophoblast cells occurs throughout gestation in both the human and mouse placentae, human Trophoblast Stem (TS) cells, which have just recently been identified, are not thought to persist beyond early development. This leaves a gap in our understanding of the mechanisms that support placental homeostasis and regenerative potential, later in pregnancy. Mouse TS cells, on the other hand, are better characterized. They have been used as an investigational model of the molecular mechanisms supporting trophoblast proliferation and differentiation, thereby contributing to our understanding of placental development and function, though they are thought to be depleted by E8.5 of a 20-day gestation. In many organs, tissue-specific stem/progenitor cells underlie homeostasis and provide an ability to adapt to stress and injury. Characterizing human TS cells could offer the 8-10% of pregnancies that encounter complications hope through regenerative medicine. Applying this logic, our lab identified increased trophoblast proliferation and expression of the TS marker, Eomes, beyond early development and have found a population of proliferative, multipotent TS-like cells using Sca-1 as a cell surface marker, in the late gestation mouse placenta. Our governing hypothesis is that placental stress confers proliferative potential to a sub-population of trophoblast, and we propose this population is critical to fetal health. The objectives of this proposal are to use cutting edge genetic and genomic techniques to study persistent TS and Sca-1+ trophoblast populations in the context of placental insufficiency and assess whether they provide the mouse placenta an adaptive mechanism. We will investigate the function of Sca-1(Ly6A) in mouse trophoblast to provide insight into the adaptive response. Additionally, we will compare the transcriptomes of mouse TS to the novel human TS cells, focusing on transcription factors and cell surface markers to define specific subpopulations to then evaluate the adaptive response of the human placenta. Ultimately, our work will determine the regenerative capacity of the placenta and aid in identifying the role human TS cells in this process, to develop new treatments for placental-related diseases of pregnancy.